Can Your Baby Wield a Machete?

The developmental milestones parents obsess over are meaningless.

My son Isaiah sat up late. He crawled late, too, according to all the books, and he agreed to walk only when he was pretty sure he wouldn't fall. With the exception of his remarkable ability to name dump trucks, garbage trucks, and every single apple in the produce section, he shows every sign of talking late, too.

Late, early, on time: In our what-to-expect era, when baby Web sites offer weekly, birthdate-timed developmental newsletters, parents can hardly avoid knowing where their child falls on the developmental spectrum. As Isaiah has stumbled through his first years, he's been accompanied, via childrearing guides and Web sites, by the phantom presence of a typical child, whose textbook development sometimes has made Isaiah seem like Leo the Late Bloomer.

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But when parents today worry about their child not meeting developmental norms, especially for motor skills, they're too often worrying needlessly. The typical child, it turns out, is a myth. But someone forgot to tell the parents.

Arnold Gesell, a pioneering developmental scientist at Yale, came up with the theory of developmental norms—the idea that there is a normal way for humans to develop—a little less than a century ago. Gesell believed that motor development was a question of neuromuscular maturation: Motor skills developed as the brain matured. It followed that all infants had to pass through the same series of developmental steps, in the same order, at the same times. Gesell just had to map what those steps were and when exactly they occurred.

He did so in astonishing, migraine-inducing detail. Using cameras to record the tiniest details of infant behavior, Gesell described the appearance of 40 different motor skills and the developmental stages of each of those skills: 23 stages of crawling, 58 stages of grasping, 53 stages of rattling. His work was rigorous, seemingly authoritative, and the basis for the first charts depicting how infants should develop. These showed babies as they moved in a strict, perfectly timed procession from lying to rolling over to sitting to crawling, and so on. Gesell's work was hugely influential: It cemented the concept of developmental norms, and the separation of normal and abnormal, into the popular consciousness. Gesell's books and the movies of infants produced by his laboratory made him famous, an early child-rearing expert. This video offers a sense of his patient, painstaking style and the quiet grandeur of his pursuit.

Yet Gesell himself knew that his norms weren't set in stone. As Ann Hulbert writes in Raising America, her magisterial history of modern American childrearing advice, he warned that norms " 'are readily misused if too much absolutist status is ascribed to them,' as he knew from having arrived at them by observing countless deviations."

But the idea of developmental norms was too seductive to be rejected. It provided parents and pediatricians with guidelines and expectations. For almost a half-century after Gesell, the proper sequence and timing of development were treated by developmental psychologists as sacred; any deviation was dangerous. For example, the theory of "neurological organization," devised by the psychologist Carl Delacato, held that if an infant failed to take the expert-marked path for motor skills, her reading and language skills would veer off course, too. New research was largely limited to creating more precise norms—to making norms yet more normative.

The problem with all of this is that the theory of neuromuscular maturation turned out to be fundamentally wrong. Even during Gesell's ascendancy, there was ample evidence of the amazing plasticity of human development. Beginning in the 1960s, developmental psychologists conducting ethnographic research in different cultures discovered that infants around the world skip various developmental stages or develop key skills more quickly (or slowly) than American children. As a classic paper showed, for example, infants in a farming village in Kenya sat up and walked far sooner than their Western counterparts, but only when raised in traditional ways, which encouraged these skills. Moreover, different cultures have their own internal sense of what's normal. In one wonderful study, English, Jamaican, and Indian mothers living in the same city were asked to predict when their newborns would reach certain motor milestones. Remarkably, each group's expectations turned out to be accurate—even though they frequently varied by several months. As the (epically cute) new Babies documentary makes clear, culture matters.

All this reflects how infants actually develop: Babies take different routes to the same destination. There's no right way to learn to walk, for example, and there's scarcely even a right time: The accurate range for when babies should start extends from 8 months to almost 20 months—an amazingly, almost meaninglessly broad stretch of time. The most interesting research on motor development in recent years treats it as the product of many different systems: the infant's environment, personality, nervous system, and personal physical limitations. When all these variables interact, you get a lot of different results, as countless studies have made clear. You don't get a chart that looks like something out of The Ascent of Man.

But the idea of the typical child is ever with us, never mind the volumes of research disproving it. As several prominent developmental psychologists have written, somewhat despairingly, "Ages and stages so thoroughly pervade our conception of motor development that every pediatrician's office and developmental textbook sports a requisite table of developmental norms." These charts and tables make us anxious and shrink our sense of the possibilities of infancy. There's no chart that can make sense of this photo of an 11-month-old Efe infant, in a rainforest in the Democratic Republic of Congo, carefully cutting a fruit in a half with a machete.

Of course, parents want some sense of what their children should be doing, and knowing that their baby girls technically might be able to use a machete won't help much. But false milestones and misleading developmental narratives aren't helping, either. It's a sorry state of affairs: Even as developmental psychologists have discarded the idea of universal developmental milestones, those milestones are the only things many parents know about developmental psychology.

We should start by erasing the word normal from the developmental vocabulary: What's typical in infancy is variation. Rather than a multitude of milestones, parents would sleep better with fewer but more relevant guidelines, an acknowledgement of how unstructured infancy actually is. At our pediatrician's office, I recently discovered a rare such example: a CDC flyer with the heading, "It's time to change how we view a child's growth." It lists a few key achievements for the end of each year, helping parents sift out actual problems. If a baby doesn't respond to "no" at the age of 1, for example—even if "responding to" just means ignoring—that's probably worth mentioning to the pediatrician.

I can report that Isaiah, who has always lagged behind his mythical normal counterpart, has met all the milestones on the CDC's short list. As a proud parent, though, I'm a little aggrieved it fails to recognize his deep talent for apple taxonomy: He's clearly way ahead of his peers.